On 10/27/2014 01:48 PM, whit3rd wrote:
On Monday, October 27, 2014 12:01:45 PM UTC-7, David Platt wrote:
In article ,
micky wrote:
How can the same FM station appear at two different spots on the dial?

(3) Intermodulation. If you have two strong stations nearby, their
signals can mix (either in the receiver front end, or elsewhere)
and create "spurious" signals located on either side of their true
locations on the dial. These spur signals will often be noisy and
distorted.

This sounds very likely; if it is due to front-end nonlinearity, it's
possible to test/treat it by inserting an attenuator between the FM antenna
and the receiver (assuming the receiver has a plug-in antenna).
Lower the signal level, and the spurious response should go away.

Alternately, one can attenuate (filter) either the interfering FM station or the (presumably
AM) difference-frequency station: this can be done with a lossy antenna+load
placed near your radio, so can apply without access to antenna terminals.


I used to work on Radio Row in Houston. One day the FCC came to visit
KILT FM 100.1 because they were causing squeals on the aeronautical
band. It wasn't any of the station's pro gear making the interference;
it was an old console FM receiver in the station lobby. 100.1 + 21.4 =
121.5. Radio row was on the direct approach to Hobby Airport or this old
mis-aligned radio would have never been busted.